A catalytic oxidative valorization of biomass-derived furfural with ethanol by copper/azodicarboxylate system

An efficient tandem process for the oxidative condensation of furfural (FUR) with ethanol catalyzed by the copper/azodicarboxylate system has been developed. Firstly, the hydrogen transferring between FUR and ethanol is investigated under the nitrogen atmosphere by combining the azodicarboxylate and alkali carbonates, in which the main products are furfuryl alcohol and furan-2-acrolein. In the following, the cuprous halides and molecular oxygen are supplemented into the reaction system in order to improve the yield of furan-2-acrolein; therein, it is found that furfuryl alcohol is further oxidized and the selectivity of furan-2-acrolein is obviously elevated when CuI and o-phenanthroline (Phen) are used as the co-catalysts. Under optimal reaction conditions, 82.5% conversion of FUR with 87.7% selectivity of furan-2-acrolein is obtained with the assistance of diethyl azodicarboxylate (DEAD) and potassium carbonate. At last, a possible catalytic mechanism is proposed for the oxidative condensation reaction between FUR and ethanol in the presence of O-2.